This invention relates generally to a process for treating the skin with light, i.e., electromagnetic radiation in the visible and infrared portions of the electromagnetic spectrum.
Exposure to x-rays and/or ultraviolet light can produce damage to skin and body tissues. This damage can produce immediate, short term or long term changes. These changes can be temporary or permanent. Benign skin changes can range from temporary irritation such as seen in radiation burns or sun burns, or can be more delayed such as radiation dermatitis or chronic sun damage (poikiloderma).
Malignant changes can include pre-cancerous lesions such as actinic keratoses or leukoplakia or cancerous changes such as squamous cell carcinoma, or basal cell carcinoma, or malignant melanoma. These changes frequently occur in the exposed tissue, but they also occur in non-exposed areas. Among the three most common skin cancers (basal cell carcinoma, squamous cell carcinoma, and melanoma), melanoma has been reported to be the most common in non-sun exposed areas, while it is the least common overall of the three skin cancers.
Procedures for preventing damage from x-rays and ultraviolet light include: avoiding exposure, and using mechanical or chemical screens to block the energy waves, as well as oral or topical products such as antioxidants, or retinoids to prevent or repair the damage before or after damage has occurred. Topical or oral chemotherapy has also been used to reverse or prevent progressive damage, precancerous or cancerous changes. Surgery with scalpels, surgical instruments or with cutting lasers has been used to remove or ameliorate damaged, precancerous or cancerous areas.
X-rays have also been used to selectively target cancers. By delivering x-ray energy to specific sites, those sites may selectively be damaged or destroyed. Even though the long-term side effects may include scarring and/or precancer and/or cancer, the beneficial shorter term clearing of the undesirable tissue may outweigh the longer-term risks. These benefits are especially valuable in the elderly patient.
Light in the visible and/or infrared spectrum has been applied to skin surfaces for purposes of treating blood vessels, pigmentary changes, and irregular surface topography of the skin (elevations and/or depressions and/or scarring). The light is applied either alone or in combination with photosensitizing agents and specifically targets chromophores such as the hemoglobin in blood, melanin in skin, or porphyrin photosensitizers that accumulate in target tissue.
Photodynamic therapy (also called PDT, photoradiation therapy, phototherapy, or photochemotherapy) is a treatment for some types of cancer. It is based on the discovery that certain chemicals known as photosensitizing agents can kill one-celled organisms when the organisms are exposed to a particular type of light. PDT destroys cancer cells through the use of light in combination with a photosensitizing agent.
In PDT, the photosensitizing agent is injected into the bloodstream and absorbed by cells all over the body. Alternatively, the photosensitizing agent may be applied topically for treating precancerous and cancerous skin. The agent accumulates more in cancer cells than it does in normal cells. When the treated cancer cells are exposed to light, the photosensitizing agent absorbs the light and produces an active form of oxygen that destroys the treated cancer cells. Light exposure must be timed carefully so that it occurs when most of the photosensitizing agent has left healthy cells but is still present in the cancer cells. The light may have a wavelength between 650-800 nm for tissue penetration purposes.
The photosensitizer used in photodynamic therapy should be partially hydrophilic for injection and delivery purposes and partially lipophilic for cell uptake purposes. Porphyrins are typically used as photosensitizers. Polarity and partition coefficient of these compounds can be altered by attaching polar residues (such as amino acids, sugars, nucleosides) onto the fundamentally hydrophobic porphyrin ring.
In December 1995, the U.S. Food and Drug Administration (FDA) approved a photosensitizing agent called porfimer sodium, or Photofrin®, to relieve symptoms of esophageal cancer that is causing an obstruction and for esophageal cancer that cannot be satisfactorily treated with lasers alone. In January 1998, the FDA approved porfimer sodium for the treatment of early nonsmall cell lung cancer in patients for whom the usual treatments for lung cancer are not appropriate. The National Cancer Institute and other institutions are supporting clinical trials (research studies) to evaluate the use of photodynamic therapy for several types of cancer, including cancers of the bladder, brain, larynx, and oral cavity. Researchers are also looking at different laser light types, photosensitizers that can be applied to the skin to treat superficial skin cancers, and new photosensitizing agents that may increase the effectiveness of PDT against cancers that are located further below the skin or inside an organ.
Researchers have investigated the effect of visible light treatments on sun-damaged skin. The investigation applied light in two periorbital treatments six weeks apart. In each session, the light had a wavelength of 590-1200 nm and was applied in two pulses each of 4.5 msec duration, with an interpulse interval of 10 msec and a total applied energy of 42 J/cm2. The researchers found an increase in cancer-destroying enzymes MMP-I, MMP-II, TIMP-II, Caspase III. The investigation uncovered a localized increased expression of protein in the fibroblasts after the treatment. The researchers suggested that the application of electromagnetic radiation to sun-damaged skin might reduce the chances of skin cancer formation and theorized that the light treatment stimulates dermal fibroblasts to increases the production of matrix metaloproteases, their inhibitors, and markers of apoptosis.